Porous electrode for air permeable moisture probe



June 8, 1965 H. L. JAMESON POROUS ELECTRODE FOR AIR PERMEABLE MOISTURE PROBE Filed Feb. 9. 1960 MEASURING CIRCUIT INVENTOR. HOWARD L.JAMESON BY/V ATTORNEY United States Patent 0 3,183,553 PGRGUS ELECTRO E EERE M9353 RE PRJP'E Howard L. .iameson, Ferndaic, Mich, assign-or to Harry W. Dietert Co., Detroit, Mich a corporation of Michigan Filed Feb. 9, H69, Ser. No. 7,552 2 tilaims. (til. 32 -51) The present invention relates to an air permeable moisture probe.

The probe disclosed herein is intended for use in systems for obtaining a compensated measurement of the moisture content of granular material. A typical example is in the measurement of the compensated moisture content of foundry sand.

The expression compensated moisture content refers to the fact that the measurement of the moisture content of the sand is carried out in such a way as to compensate for one or a number of different circumstances or conditions. In other words, it is not intended to provide a true and direct reading of the moisture content.

The measurement of compensated moisture contents is more fully disclosed in prior application of Randolph L. Dietert, Serial No. 845,727 (now Patent 3,161,927, dated December 22, 1964), and the application of Harry W. Dietert and Randolph L. Dietert, Serial No. 860,749, (now Patent 3,046,624 dated July 31, 1962). However, for completeness herein, measurement of two different compensated moisture contents will be described generally.

The measurement of compensated moisture content involves the step of effecting a predetermined drying action on a specimen of moist granular material just prior to measuring the actual moisture content of the partially dried specimen. The partial drying of the specimen may be in accordance with a number of different conditions. In the first place, it may be carried out in such a way as to represent a drying action which is dependent upon the actual temperature of the moist granular material. This may be important in foundry sand which may be available at widely varying temperatures. In some cases for example, the foundry sand is re-used before cooling to room temperature, in which case it may carry a substantial amount of super-heat from a previous casting operation. The usual purpose of measuring the moisture content of foundry sand is to insure that it contains the proper amount of moisture when it is to be used for forming a mold. The amount of moisture which will be lost between the measurement of its moisture content and its subsequent use will in general be influenced substantially by its temerature when its moisture content is measured.

The passing of drying air capable of absorbing moisture from the moist granular material through at least that portion of a specimen whose compensated moisture content is to be measured, will result in removal of moisture from the specimen which is variable directly in accordance with its instantaneous temperature. Accordingly, when a reading of its moisture content is made, this reading will be of a moisture content which will exist throughout the quantity of moist granular material at a predetermined later instant due to loss of moisture by evaporation as determined largely by its temperature.

The foregoing method of measuring moisture content of granular material compensated for the instantaneous temperature thereof is disclosed in detail in the above identified application Serial No. 845,727.

A measurement of moisture content compensated for ambient weather conditions as well as temperature of the granular material is also possible. In this case the drying characteristics of the air passed through the specimen will be related to weather conditions so that its drying action will be directly dependent on the same weather conditions which will influence loss of moisture from the granular material during the interval between moisture measurement and the time of its subsequent use in forming a mold. For example, either the temperature, or the moisture content or humidity of the drying air, or both, may be controlled in accordance with room temperature, room humidity, or both.

This method of compensating for subsequent evaporation of moisture from the granular material due in part to room temperature and/ or humidity, is fully disclosed in application Serial No. 860,749.

In both of the methods referred to above, the measurement of moisture con-tent is determined by a probe which includes an electrode separated by insulating material from a second electrode or ground connection. The granular material whose moisture content is to be measured is pressed against the probe. Dependent upon the particular circuitry involved, the measurement of moisture content may be by determining an electrical property of the granular material between the electrodes, or the first electrode and the ground connection. For example, the electrical property variable in accordance with mois ture content may be the resistance of the granular material, or it may be the electrical capacitance thereof.

in accordance with the present invention the insulated electrode is formed of a porous metallic conductor and has associated therewith means for passing drying air through the pores of the electrode.

With the foregoing general description in mind, it is an object of the present invention to provide a moisture robe comprising a porous metal electrode.

It is a further object of the present invention to provide a moisture probe comprising a porous metallic electrode, means for connecting the electrode into an electrical circuit, and means for supplying a fiow of drying air to pass through the electrode.

It is a further object of the'present invention to provide a moisture probe adapted to operate in contact with moist granular material compressed against the active surface of the probe, the probe including a porous metallic electrode having an exposed surface adapted to be engaged by the compressed granular material, means insulating the electrode from a second electrode or ground connection, means for connecting the electrode into an electrical measuring circuit, and means for inducing a flow of drying air through the electrode and through the surface thereof adapted to be in contact with the'compressed granular material. 7

More specifically, it is an object of the present invention to provide a system for obtaining a measurement of compensated moisture content of granular materialwhich comprises a mixer, a moisture probe located in a wall of the mixer adapted to be contacted by granular material therein, means for applying granular material to the surface of the probe, and means operable a predetermined time after application of the granular material to the surface of the probe for compressing the granular material against the surfce of the probe, the probe including a porous or air permeable electrode of metallic metal, means for connecting the electrode into an electrical measuring circuit, and means for supplying drying air to the electrode in such a way as to cause it to pass through the electrode and particularly through the surface thereof adapted to be contacted by the granular material. a

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawing, illustrating a preferred embodiment of the invention, wherein:

The figure is a sectional view through an air permeable Fatented June 8, 1965' if.) moisture probe constructed in accordance with the present invention.

The moisture probe disclosed in the figure may conveniently be provided. in the bottom wall of a sand mixer or muller so that it will be contacted by the sand in the mixer. Preferably, the probe is located intermediate the center and a side wall of the mixer, and means are provided for alternately depositing a specimen of sand or other granular material on the probe, after a predetermined interval compressing the specimen against the surface of the probe, and thereafter removing the compressed specimen from the probe prior to depositing a second specimen against the probe surface. The foregoing is accomplished simply by providing a rotary structure which includes one or more scrapers 1G movable about a vertical axis and preferably in slightly spaced relation above the bottom wall 12 of the mill. Associated with the scraper, or scrapers It) is one or more relatively heavy rollers, a portion of one of the rollers being indicated at 14. If it is assumed that the rollers 14 and scrapers it) are moving across the upper surface of the probe to the left as seen in the figure, it will be observed thatthe portion of the granular material indicated at 16 directly above the probe has been compressed by the passage of the roller 14 and will shortly be removed by passage of the scraper 10. Accordingly, the drying interval which commences when the moist specimen is deposited on the electrode 39 and which in effect terminates when the roller 14 compresses the specimen against the roller, is a predetermined interval so that the amount of drying can be predetermined. In this connection it may be mentioned that the compressed specimen is slid oif'the surface of the probe by passage of the scraper without requiring actual mechanical contact between the scraper and the surface of the probe.

Moreover, it will be observed that as the scraper passes over the active surface of the probe and removes the previously measured compressed specimen therefrom, sand or other granular material will drop down onto the upper surface of the probe as soon as the scraper has passed. This material provides a new specimen which is in contact with the surface of the probe.

If the scrapers and rollers are positioned a predetermined distance apart and the mechanism supporting the same is rotated at a predetermined rate, it will of course be apparent that the new specimen of granular material which drops by gravity onto the surface of the probe as soon as the scraper it) has passed, will remain in contact with the surface of the probe for a predetermined brief interval before it is compressed against the surface of the probe by the succeeding passage of a roller.

Moreover, it is a characteristicof a probe of the type disclosed that a maximum reading will be obtained when the material is compressed against the probe. Therefore, the operation as suggested above provides a predetermined interval after application of an uncompressed specimen to the surface of the probe before it is actually compressed against the probe to obtain a maximum reading of moisture content.

In accordance with the present invention, the probe proper comprises a plate 18' which is recessed as indicated at 29 into the upper surface of the bottom wall 12 of the mixer. The plate 20 is in contact with the outer surface of a tubular metal member 22, the upper end of which is recessed as indicated at 24 for the reception of an insulating body 26 which may be formed of a plastic material such as Teflon. The insulating body as is in turn recessed at its upper end as indicated at 28 for the reception of the air permeable electrically conducting electrode. 30 which .will subsequently be described in detail.

The recess 28 formed in the upper end of the insulating body 26 has a bottom wall as indicated at 32 pro vided with a plurality of vertically extending passages 34 for a purpose which will presently appear.

Extending longitudinally through the metal member or tube 22 is a conducting rod 36, the upper end of which is threaded as indicated at 33 and screwed into a tapped opening at the lower end of the electrode 39. The rod 36 extends through an opening 40 provided in the bottom wall 32 of the insulating body 26.

At its lower end the rod 36 is supported in an insulating bushing 42 which is received in a recess 44 formed at the lower end of the tube 22. As indicated in the figure, the rod 36 constitutes a conductor and is adapted to be connected by an electrical connector 46 to a moisture measuring circuit indicated at 48.

it will be observed that the rod 36 is supported in insulated relation in the axially extending passage 50 in the tube 22, thereby providing an annular air passage 2 which is in communication with the lower end of the plurality of passages 34 extending through the bottom wall of the insulating body 26 and in communication at their upper ends with the lower surface of the air permeable porous electrode.

Attention is called to the fact that the porous electrode 3%? has its upper fiat surface exposed in the tank and that the entire remainder of the electrode is enclosed by the insulating body 26 and the tube 22 which together comhim with the electrode to define a pressure chamber made up of the air passage 52 and the passages 34. As will subsequently be described, air admitted under pressure to the pressure chamber is thus forced through the porous electrode and escapes from its exposed upper flat surface.

A conduit 54 is provided which communicates with the annular passage 52 and which is connected to a source of drying air here indicated diagrammatically as a pump 56. It will be appreciated that the drying air supplied under pressure by the pump 56 to the passage 52 at the interior of the tube 22 may be supplied at a constant relatively low temperature and substantially completely devoid of moisture, in order to carry out the moisture content compensation based upon the existing temperature of the granular material. Alternatively, the air supplied under pressure by the pump 56 may have its temperature and/ or its moisture content or humidity controlled in accordance with the temperature and humidity of the room air so as to provide a moisture compensation dependent upon ambient temperature and/or air humidity.

Referring again to the air permeable electrode 3%, this electrode may be formed from metallic particles or powder interconnected by sintering or the like so as to provide a highly electrically conducting body and one which at the same time permits a very substantial flow of drying air therethrough. The air permeability or porosity of the electrode 30 may be controlled within rather wide limits by selection of the particle size of the metal, initial compression applied to the metal, and the conditions of sintering. Obviously of course, the larger the particle size, other things being constant, the greater the air permeability.

The use of an electrode in the probe which is permeable to drying air substantially uniformly across its face, has a substantial advantage in its use as disclosed herein. The air forced through the permeable electrode under substantial pressure flows out through a multiplicity of pores opening into the exposed surface of the electrode and hence, the entire area of the sand or other granular material which has been deposited on the surface is subjected throughout its entire extent to a corresponding multiplicity of drying jets of air. The air which passes outwardly from the pores in the active surface of the electrode tends to move laterally or to plane between the exposed surface of the electrode and the adjacent surface of the granular material. Since this air is introduced through a large number of tiny pores or orifices, the construction avoids the tendency to blow the adjacent granular material away from the surface of the electrode, which would be the case if the air were introduced through a relatively small number of relatively large ports or openings.

By using the porous metallic electrode it is possible to obtain the foregoing compensation effect during the very brief interval in which the specimen is actually being compressed by the passage of the roller. In mixers or mullers of the type described the rollers are relatively large and relatively heavy, and are allowed to float vertically. Moreover, the movement of the rollers is relatively slow. Therefore, as the roller passes over the surface of the probe the moist granular material is compressed in a gradual manner, reaching maximum compression as the center line of the roller passes directly over the probe.

As previously mentioned, the electrical measuring circuit tends to indicate a maximum moisture content at the instant of maximum compression, other factors being equal. In the present case, as the compression of the moist granular material increases to a maximum during passage of the roller over the probe, the granular material in direct contact with the porous metallic probe is at the same time being subjected to a drying action. Accordingly, as the center line of the roller passes over the probe the instantaneous reading or indication of moisture is determined by the compression of the specimen, which has then reached the maximum; and by the residual moisture content of the specimen resulting from removal of some of the moisture from the portion of the specimen in contact with the surface of the probe as a result of the passage of drying air through the electrode to the said portion of the specimen, principally as the specimen was undergoing the increasing compression due to passage of the roller.

The drawings and the foregoing specification constitute a description of the improved air permeable moisture probe in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

1. Apparatus for determining a compensated moisture content of granular material which comprises a mixer for receiving the granular material, a compensating probe in a wall of said mixer, first means in said mixer for repeatedly depositing moist specimens of granular material against said probe and after a predetermined interval removing them, second means for compressing said specifor receiving the granular material, a compensating probe in a wall of said mixer, said probe comprising a porous electrically conducting electrode, said electrode being a V shaped body consisting of sintered metallic particles,

mean for connecting said electrode to a source of electrical potential, means for blowing drying air through said porous electrode, means for depositing a moist specimen of granular material against said probe in uncompressed condition, said drying air efiecting a predetermined drying effect on the portion of said specimen next to said probe, means for compressing said specimen against said probe after a predetermined short interval to obtain a maximum reading of an electrical, condition thereof on a detector connected to said probe, and means for thereafter removing said specimen from said probe, the means for depositing a moist specimen and removing the specimen comprising a scraper, the means for compressing the specimen comprising a roller-spaced from the scraper and rotatable in the mill therewith to provide for compressing the specimen after a predetermined interval of drying thereof, said probe being located in the bottom wall of said mixer, whereby passage of said scraper in removing a previous specimen permits an uncompressed portion of granular material to drop on said probe by gravity to form the next succeeding specimen.

Reterenees Cited by the Examiner UNITED STATES PATENTS 2,217,626 10/40 Strang et al. 324- 2,329,840 9/43 Keinath 73-27 2,539,355 1/51 Reichertz 324-.65 X 2,886,868 5/59 Dietert et al 324-65 X 2,941,174 6/60 Richards 73-73 X 2,957,130 10/60 Dietert et al. 324-465 3,047,801 7/ 62 Dietert 324 -61 WALTER L. CARLSON, Primary Examiner.

c. E. OCONNELL, Examiner. 

1. APPARATUS FOR DETERMINING A COMPENSATED MOISTURE CONTENT OF GRANULAR MATERIAL WHICH COMPRISES A MIXER FOR RECEIVING THE GRANULAR MATERIAL, A COMPENSATING PROBE IN A WALL OF SAID MIXER, FIRST MEANS IN SAID MIXER FOR REPEATEDLY DEPOSITING MOIST SPECIMENS OF GRANULAR MATERIAL AGAINST SAID PROBE AND AFTER A PREDETERMINED INTERVAL REMOVING THEM, SECOND MEANS FOR COMPRESSING SAID SPECIMENS AGAINST SAID PROBE AT PREDETERMINED INTERVALS AFTER DEPOSIT OF SAID SPECIMENS ON SAID PROBE, SAID PROBE COMPRISING A POROUS ELECTRICALLY CONDUCTING ELECTRODE, SAID 